Conditioning treatment of magnesium for electroplating



Patentecl Apr. 1 5 1947 CONDITIONING TREATMENT OF MAG- NESIUM FOR ELECTROPLATING Harvey Eugene Wagoner, Niagara Falls, N. Y., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application April 9, 1942,

7 Serial No. 438,305

7 Claims. (Cl. 204-29) This invention relates to the electroplating of metals and more particularly to the conditioning of magnesium and alloys of magnesium for electroplating.

Heretofore no satisfactory method for electroplating on magnesium or alloys in which'magnesium is theprincipal constituent was known. Ordinary methods of electroplating, for example, those utilizing cyanide plating baths fail to produce an adherent plate of metal, such as copper, cadmium, silver, gold, brass, and zinc, on magnesium. Although such metal may be deposited on magnesium by conventional means, the resultant plate is easily cracked and fails to adhere upon bending or working. 7

It is one of the objects of thi invention to pro- ,vide a new and improved process for electroplating on magnesium and alloys of magnesium. Another object is to provide a novel process for the conditioning of magnesium andalloys of magnesium for electroplating whereby conventional electroplating baths will produce a uniform and adherent plate. These and other objects will be apparent from the following description of my invention.

The above objects are attained, in accordance with my invention, by contacting magnesium or alloys of'magnesium in which the magnesium is the principal constituent with 'a bath comprising a. monobasic unsaturated aliphatic acid containing at least one doublebond, an aliphatic ester of said acid, or a heavy metal salt of said acid at elevated temperatures prior to electroplating.

I have discovered that when magnesium is treated in a bath'comprising one or more of the above conditioning agents, the metal is so conditioned that a uniform, adherent plate is readily obtained by means of conventional alkaline plating baths, such as cyanide plating baths.

In the operation of my novel process the metal to be conditioned is first cleaned in order to remove the surface coating which is always present on magnesium which has been exposed to the atmosphere. This may be done by any well-known method, for instance, by sanding. The metal may then be degreased, if necessary, by any suitable method, for instance by the use of chlorinated hydrocarbon degreasing baths containing trichlorethylene, perchlorethylene, or other degreasing solvents. After removal from the degreasing bath and drying, the metal to be conditioned is then treated in a bath containing one or of these acids.

mately 250 C. for about five minutes. The magnesium strip may then be removed from the conditioning bath and the excess conditioning agent wiped off. The magnesium may then be electroplated by treatment in a cyanide'electroplating bath.

Typical electroplating procedure may be illustrated as follows: The metal is first given a conventional copper strike and then plated in a copper cyanide plating bath containing about 12 oz. per gallon of CuCN. The magnesium is plated in this bath for about ten minutes at a current density of around 50 amperes per'square foot. The electroplating treatment described is to be considered illustrative of typical plating procedure and various other well-known alkaline electroplating baths may be utilized.

Among the metals which may be plated on magnesium or an alloy thereof, in accordance with my invention, are copper, zinc, cadmium, silver, gold, and tin. Brass may also be satisfactorily plated and excellent results may be obtained by electroplating any of these metals on magnesium utilizing well-known alkaline plating baths, for example, cyanide plating baths commonly utilized in the art, subsequent to treatment of the magnesium in accordance with my novel conditioning rocess.

I have found that in general the magnesium to be plated should be exposed to contact with the conditioning agent fora period of about five to thirty minutes. While longer periods of time may be utilized, I have found that in general no advantage is gained thereby. A treatment for less than five minutes may in some cases be satisfactory but usually is insufiicient for best results.

The temperature of the conditioning treatment may vary over a wide range with satisfactory results. However, I have found that temperatures above C. are desirable and'I prefer to operate my conditioning treatment at temperatures of 200 to 300 C. The treatment may conveniently be carried out at temperatures somewhat below the boiling point of the conditioning agent utilized, although this is not essential.

The compounds which I have found to .be suitable as conditioning agents in the process of my invention include the monobasic unsaturated aliphatic acids having at least one double bond, aliphatic esters of these acids and heavy metal salts Illustrative of the acids which I have found satisfactory are crotonic, erucic, oleic, linoleic, brassidicelaidic, angelic, acrylic, vinyl acetic, clupanodonic, geranic, and linolenic acids. Among the suitable esters may be mentioned methyl oleate, butyl crotonate, octyl linoleate, allyl crotonate, geranyl oleate, crotyl erucate, the ethyl ester of elaidic acid, glyceryl oleate, glyceryl linoleate, and propenyl linoleate. Among the suitable heavy metal salts are copper oleate, zinc oleate, lead linoleate and various other heavy metal salts. The heavy metal salts included within the scope of my invention as defined in the claims are the salts formed by any of the metals capable of forming salts with the specified aliphatic acids except the alkali or alkaline earth metals.

Although the above classes of compounds are suitable in the process of my invention, I have found that particularly good results are obtained with oleic acid, linoleic acid and copper oleate, and I prefer to utilize one or more of these compounds which are readily available and which produce consistently excellent results. The following examples are illustrative of my invention:

Example I A strip of magnesium is sanded and then degreased in a bath of trichlorethylene. After removal from the degreasing solvent, the magnesium is dried and immersed in a bath of linoleic acid mantained at 250 C. during five minutes. The magnesium is then wiped free of excess linoleic acid and subjected to a regular copper strike treatment followed by electroplating in a conventional cyanide plating bath. A uniform, adherent copper plate is obtained.

Example II A strip of magnesium alloy composed of 6% aluminum, 0.2% manganese and the balance magnesium is sanded and then degreased in a bath of trichlorethylene. After removal from the degreasing solvent the alloy is dried and immersed in a bath of linoleic acid maintained at 250 C. during five minutes. The alloy is then wiped free of excess linoleic acid and subjected to a regular copper strike treatment followed by electroplating in a conventional cyanide plating bath. A uniform, adherent copper plate is obtained.

Example III An alloy composed of 6% aluminum, 3% zinc, 0.15% manganese and the balance magnesium is prepared as in Example I and then immersed in a bath of oleic acid maintained at 280 C. during ten minutes. The alloy is then wiped free of excess oleic acid and plated as in Example I. An excellent, adherent copper plate is obtained.

Example IV A strip of magnesium prepared as in Example I is immersed in a bath of copper oleate maintained at 200 C. during twenty minutes. Upon removal of excess copper oleate and subjection to a plating treatment as in Example I, an excellent protective copper plate is obtained.

Example V A strip of magnesium prepared as in Example I is immersed in a bath of linoleic acid maintained at 230 C. during five minutes. At the end of this treatment, excess linoleic acid is removed from the magnesium and the strip electroplated with zinc. A uniform plate of zinc is thus obtained.

Example VI A strip of magnesium is prepared as in Exam pic I and then immersed in a bath of glyceryl oleate maintained at 270 C. during ten minutes".- Upon ubsequent electroplating as in. Example I a uniform, adherent plate of copper is obtained.

Examp e VII A strip of magnesium prepared as in Example I is immersed in a bath of butyl 'crotonate maintained at 180 C. during twenty-five minutes.

' Anadherent copper plate is obtained upon subjecting the conditioned magnesium strip to an electroplating treatment as in Example I.

Example VIII A strip of magnesium prepared as in Example I is immersed in a bath of copper linoleate maintained at 260 C. during fifteen minutes. Upon removal of excess copper linoleate and plating in a cadmium cyanide electroplating bath a uniform, adherent cadmium plate is obtained.

Example IX A strip of magnesium is sanded and degreased as in Example I and then immersed in a bath of brassidic acid maintained at 275 C. during ten minutes. The excess brassidic acid is removed and a firm, adherent silver plate is obtained by treatment in a cyanide plating bath.

Example X A strip of magnesium is sanded and degreased and then immersed in a bath of zinc oleate during five minutes. After removal of excess zinc oleate the magnesiumstrip is plated as in Example I. An excellent, adherent copper plate is obtained.

The process of my invention is extremely valuable in providing a method whereby a protective coating of metals may be applied to magnesium or alloys of magnesium, since heretofore no satisfactory method was known for accomplishing these results. Strips or sheets of magnesium, which are plated in accordance with the process of my invention, may be bent, buffed and worked without causing chipping or cracking o the plate.

Various modifications of the process of my invention may be made without departing from the scope thereof. For example, various combinations and mixtures of the conditioning agents disclosed may be utilized and various changes in procedure, which willbe apparent to those skilled in the art, may be made.

I claim:

l. The process for electroplating a metal selected from the group 'consisting ofmagnesium and alloys of magnesium which comprises contacting said metal with a bath comprising essentially a compound selected from the group consisting of monobas'ic unsaturated acids containing at least one double bond, aliphatic esters of said acids, and heavy metalsalts of 'said acids at temperatures above about C; but not higher than about 300 C., for aperiod of about 5 to 30 minutes said compound being in the liquid state at the operating temperature, wiping said metal and thereafter electroplating said metal with a heavy metal selected from the group consisting of' copper, zinc, cadmium, tin, silver; and gold; from an alkaline plating bath.

2. The process forv electroplating 'a metal selected from the group consisting of magnesium and alloys of magnesium which comprises contactin'g said metal with a bathcomprisingessentially linoleic 'acid at temperatures above about 100 C. but 'not higher than about 300 'C., for a ed from the roup consisting of magnesium and alloys of magnesium which comprises contacting said metal with a bath comprising essentially oleic acid at temperatures above about 100 C.

but not higher than about 300 C. for a period of about 5 to 30 minutes, said oleic acid being in the liquid state at the operating temperature, wiping said metal and thereafter electroplating said metal with a heavy metal selected from the group consisting of copper, zinc, cadmium, tin, silver, and gold, from an alkaline plating bath.

4. The process for electroplating a metal selected from the group consisting of magnesium and alloys of magnesium which comprises contacting said metal with a bath comprising essentially copper oleate at temperatures above about 100 C. but not higher than about 300 C. for a period of about 5 to 30 minutes, said copper oleate being in the liquid state at the operating temperature, wiping said metal and thereafter electroplating said metal with a heavy metal selected from the group consisting of copper, zinc, cadmium, tin, silver, and gold, from an alkaline plating bath.

5. The process for electroplating a metal selected from the group consisting of magnesium and alloys of magnesium which comprises contacting said metal with a bath comprising essentially linoleic acid at temperatures above about 100 C. but not higher than about 300 C. for a period of about 5 to 30 minutes, said linoleic acid being in the liquid state at the operating temperature, wiping said metal and thereafter electroplating said metal with copper from an alkaline plating bath.

6. The process for electroplating a metal selected from the group consisting of magnesium and alloys of magnesium which comprises contacting said metal with a, bath comprising essentially oleic acid at temperatures above about C. but not higher than about 300 C., for a period of about 5 to 30 minutes said oleic acid being in the liquid state at the operating temperature, wiping said metal and thereafter electroplating said metal with copper from an alkaline plating bath.

7. The process for electroplating a metal selected from the group consisting of magnesium and alloys of magnesium which comprises contacting said metal with a bath comprising essentially copper oleate at temperatures above about 100 C. but not higher than about 300 C., for a period of about 5 to 30 minutes said copper oleate being in the liquid state at the operating temperature, wiping said metal and thereafter electroplating said metal with copper from an alkaline plating bath.

HARVEY EUGENE WAGONER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,978,112 Malby Oct. 23, 1934 2,229,236 Beck' Jan. 21, 194.1 1,477,922 Wollner et al Dec. 18, 1923 FOREIGN PATENTS Number Country Date 29,161 British 1913 463,511 British Apr. 1, 1937 OTHER REFERENCES Metal Industry, Aug. 24, 1928, Hughes, p. 173. (Copy in 204-33.)

Manual of Industrial Chem.,1by Rogers, vol. II, pp. 924 and 933, 4th ed., 1925. (Copy in Div. 3 of the P. O.) 

